Fisher FIELDVUEDVC6200f Instruction Manual page 274

DVC6200f Digital Valve Controller
OS Function Block
February 2017
Limit Handling
The splitter function block is designed to combine the limit information from the two downstream blocks into limits
for the upstream block. The general principle is to allow the upstream block to continue control for as long as possible.
The upstream block is high‐limited (BKCAL_OUT of the Splitter block has high‐limited status) when:
D Both downstream blocks are high‐limited (both BKCAL_INS of the Splitter block have high‐limited status)
or
D One downstream block is high‐limited, the associated output slope is positive, and the other block has Bad status or
is not in Cas mode
or
D One downstream block is low‐limited, the associated output slope is negative, and the other block has Bad status or
is not in Cas mode
or
D SP is greater than or equal to X22
The upstream block is low‐limited when:
D Both downstream blocks are low‐limited
or
D One downstream block is low‐limited, the associated output slope is positive, and the other block has Bad status or
is not in Cas mode
or
D One downstream block is high‐limited, the associated output slope is negative, and the other block has Bad status
or is not in Cas mode
or
D SP is less than or equal to X11
265. Input to Output Mapping
The relationship of each output to the input may be defined by a line. Each line may be defined by its endpoints.
Examples of graphical representations of OUT_1 and OUT_2 vs. SP are shown in figure E‐18 for a split range and a
sequencing application.
The block has the same SP structure as the PID block, except that there is no limiting applied to the SP. The SP may be
used in Auto mode for testing. The operator would use the output of the PID to accomplish the same purpose. Each
downstream block can be taken out of cascade if it becomes necessary to gain control of them.
The examples shown in figure E‐18 do not show the full range of possibilities. The lines could overlap like an X, or both
start from the origin but have different slopes. The endpoints do not have to lie within 0-100%. Limits in the external
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Instruction Manual
D103412X012